In regard to organic electronic devices and circuits thereof, various package structures are known. These structures are generally configured to include a substrate; a cover; an organic active component part disposed between the substrate and the cover, such as a light emitting diode; and a sealing material for sealing the organic active component part and also bonding the substrate and the cover. One or both of the substrate and the cover are produced from a transparent material, for example, transparent glass or a transparent plastic, and can transmit light. The substrate and the cover may be flexible, and any one of them may also be constructed from steel, in addition to glass or a plastic. According to a certain embodiment in which the organic active component part is formed on a substrate, the organic active component part is covered with a coating film composed of an inorganic barrier film or of a multilayer barrier film having inorganic and organic layers laminated together. The coating film protects the surface and the periphery of the organic active component part. The sealing material may be applied or pasted on the organic active component part; however, in a case in which a coating film is available, the sealing material may be applied or pasted thereon. Such a sealing material wraps up the organic active component part and thereby fills the space between the substrate and the cover, and the sealing material affixes the substrate to the cover.
However, the organic active component parts are prone to deterioration by low molecular weight components, oxygen or water vapor. For example, an organic electroluminescent device is composed of an anode, a light emitting layer and a cathode, and a metal layer having a low work function is utilized as the cathode, so that efficient electron injection and a low operating voltage are guaranteed. A metal having a low work function is chemically reactive with oxygen and water vapor, and such a reaction shortens the service life of a device. Furthermore, oxygen and water vapor react with organic luminescent materials and thereby suppress light emission. In order to prevent the occurrence of such a reaction, a coating film is provided on the surface of an organic active component part in many cases as described above. However, it is difficult to suppress pinholes with an inorganic barrier film, and the inorganic barrier film cannot perfectly shield an organic active component part from oxygen or water vapor coming from the outside. Therefore, a sealing material that wraps an organic active component part is designed so as to be able to suppress permeation of oxygen and water vapor, particularly water vapor, coming from the outside, irrespective of the presence or absence of a coating film.
Regarding such a sealing material, a film-like curable sealing material can be used (see, for example, Patent Document 1). Generally, a film-like sealing material is provided between two support films, and after one of these support films is removed, the exposed film-like sealing material is adhered to any one of the cover or the substrate by pressing or by heating and pressing. Thereafter, the other support film is removed, and the cover and the substrate are adhered to each other. The film-like sealing material is cured by ultraviolet irradiation or heat, if necessary.
Furthermore, a liquid sealing material can also be used as such a sealing material (see, for example, Patent Document 2). Generally, a liquid sealing material is applied on the entire surface of any one of a cover or a substrate, and then similarly to the film-like sealing material, the cover and the substrate can be adhered to each other by pressing or by heating and pressing the other one of the cover or the substrate. A liquid sealing material generally needs curing, and is cured by ultraviolet radiation or heat.
A film-like sealing material generally has a viscosity that is higher than that of a liquid sealing material at room temperature. When a film-like sealing material is used at room temperature, wetting toward a substrate or a cover is poor. Also, in some cases, the sealing material hardly flows, and air is trapped between the sealing material and the substrate. In order to fluidize the sealing material and to minimize the amount of trapped air by achieving satisfactory wetting, it may be considered to paste the film-like sealing material at a high temperature. The heating temperature may exceed 100° C., and thus, a special apparatus is needed. Furthermore, a film-like sealing material requires the use, removal and disposal of support films.
Regarding the liquid sealing material, a sealing material using a compound resin having an epoxy group or an oxetanyl group (see, for example, Patent Document 2), a sealing material using a cyanoacrylate-based monomer which is ionically polymerizable (see, for example, Patent Document 3), and a sealing material using a bisphenol type epoxy acrylate and an epoxy resin (see, for example, Patent Document 4) have been disclosed. However, these have an insufficient effect of suppressing the permeation of water vapor and insufficient bending resistance after being cured. Thus, as a sealing material having a high effect of suppressing the permeation of water vapor and excellent bending resistance after being cured, a sealing material formed from a hydrogenated polybutadiene having its ends modified with a group having a urethane bond and a (meth) acrylate group (see, for example, Patent Document 5) has been disclosed.